An image sensor is a semiconductor device for converting an optical image into an electrical signal. An image sensor can generally be classified as a charge coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor (CIS).
A CIS includes a photodiode and a metal oxide silicon (MOS) transistor for each unit pixel, and sequentially detects an electrical signal of the unit pixel in a switching manner to generate an image.
Typically, the CIS includes a photodiode region for converting a light signal into an electrical signal and a transistor for processing the electric signal where the photodiode and transistor are horizontally arranged on a semiconductor substrate.
The photodiode of the horizontal type CIS is horizontally adjacent to the transistor on the substrate. Therefore, an additional area of the substrate for each pixel is required for forming the photodiode region.